Draw dies and draw presses are used to form part shapes in sheet metal forming operations. Toggle draw operations use double action draw presses with a stationary die attached to the bolster, a binder reciprocated by an outer ram and a draw punch reciprocated by an inner ram. Stretch draw operations use a stationary punch attached to the bolster, a binder supported on nitrogen cylinder cushion on the bolster and a draw die reciprocated by the press ram relative to the punch. The binder is engaged by the draw die and compresses the cushion as the die draws the sheet metal blank over the punch.
Single action draw operations are generally faster and require simpler automation systems because the panel is in the same top/bottom orientation as the subsequent trimming, flanging, and other operations in line after the drawing operation. Single action draw operations also offer the advantage of reducing the potential for collecting debris.
One disadvantage of single action draw operations is that energy is consumed by the die driving the binder against the cushion. The higher tonnage and greater speed causes additional impact between the binder and the die when the binder is set and at the end of the draw operation. The impact at the end of the drawing operation may create problems relating to picking up the part. The cushion takes up die opening space and limits the height of the total tool travel.
This disclosure is directed to solving the above problems and other problems as summarized below.